Brazil-Malvinas Confluence in the South-West Atlantic Ocean: phytoplankton species, life forms and trophic mode

Abstract The Brazil-Malvinas Confluence (BMC) is characterized by high environmental variability and represents a hotspot of phytoplankton biodiversity. This study has investigated the phytoplankton composition in the BMC and a Cold Core Eddy (CCE), with particular reference to the life forms and trophic modes of the species. Vertical hauls were performed between the maximum chlorophyll depth and the surface with a 20-μm mesh plankton net at six sampling points in the BMC (4 hauls) and CCE (2 hauls) during the austral spring (November 2019). Temperature and salinity were determined in situ. The Brazil Current and Malvinas Current in the BMC had different species compositions, and the CCE had greater similarity with the Malvinas Current. Autotrophic organisms (mainly diatoms) and marine planktonic oceanic and/or neritic life forms were predominant in the BMC and the CCE. Heterotrophic dinoflagellates were predominant in the Brazil Current and the CCE, while mixotrophic dinoflagellates in the Malvinas Current were associated with low temperatures and salinities. A high diversity of species was confirmed in the region, mainly associated with marine planktonic oceanic and/or neritic species, and there was a predominance of autotrophic organisms. The temperature conditions in the CCE promoted an increase in species richness in the region.